Hybrid vehicles are vehicles with two or more power sources in a drivetrain. For example and without limitation, a hybrid vehicle may be a gasoline-electric hybrid (“HEV”) having an internal combustion engine and an electric motor/generator. Hybrid vehicles may use both an engine and a motor to improve fuel consumption, emission, and performance by switching between the two power sources at optimal times or using a combination of the two depending on the hybrid system and vehicle mode.
HEVs are generally classified by the division of power between sources. Both sources may operate in parallel to simultaneously provide torque to the powertrain, or they may operate in series with the first source providing the torque and the second source used to augment the first source's power reserve.
HEVs also capture and store energy when the vehicle is experiencing powertrain braking. The electric motor functions as a generator and absorbs energy generated as a result of the powertrain braking and converts the energy to electric energy which may be used to increase the state of charge of a battery. Regenerative powertrain braking may be desirable beyond recouping energy because the HEV's energy may be dissipated with minimal or no negative torque supplied by the frictional wheel brakes, thus reducing wear on the frictional wheel brakes.
During regenerative braking, driver braking torque demand may be provided solely by regenerative braking or in combination with frictional braking. The apportionment of driver braking torque demand between frictional braking torque and regenerative braking torque (i.e., negative input torque via the motor) may be balanced throughout braking events to achieve as much regeneration as possible so that the energy may later be used to propel the vehicle and thereby improve fuel economy.
Near the conclusion of a regenerative braking event as the vehicle slows to low speed or comes to a stop, the braking torque supplied by the motor may be transferred to the friction braking system to avoid a disruption in the vehicle total braking torque when the bypass clutch disengages. This transfer may happen over a period of time to ensure smooth driving and driver satisfaction. This regenerative torque “blend-out” may be coordinated with the torque converter clutch disengaging. During the blend-out procedure, a controller(s) may cause the regenerative torque to decay and simultaneously increase the resistance of the friction brakes at a countervailing rate when the vehicle decelerates to low speeds.
Some HEVs may have more than one independent control logic for coordinating blend-out. These control logics may be based on different capacities and may have different objectives. As such, the independent blend-out requests may need to be arbitrated and the motor commanded accordingly.